Device and method for determining proportions of body materials

ABSTRACT

The present invention provides a radiation device that includes a device for retaining therein the body part in a uniform position. In addition, at least two reference materials that have attenuation characteristics are used and retained in the retaining device. The reference materials are being positioned for the comparative determination during a simultaneous irradiation of the body part and the reference materials. The attenuation characteristics of the reference materials are selected in correspondence to the attenuation characteristics of the body materials in the body part. A radiation device for simultaneously irradiating the body part and the reference materials is used to create attenuated beams. A detector is used to detect the attenuated beams as attenuated values. A calculating device is included for calculating the proportion of the body materials that define a particular body part of interest based on the attenuated values of the materials and the body part.

REFERENCE TO RELATED APPLICATIONS

This application is continuation of parent application Ser. No.09/848,922 filed on e May 4, 2001 now U.S. Pat. No. 6,516,045.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was supported in part by grant number BC99540 from theDepartment of the Army Medical Research Division. The U.S. Governmenthas certain rights in the invention.

FIELD OF THE INVENTION

This invention relates generally to radiography. More particularly, thepresent invention relates to a device and method for measuringproportions of body materials in body parts of humans and animals.

BACKGROUND

The determination of proportions or densities of different bodymaterials in body parts of humans or animals is of utmost importance tomonitor, for instance, cancer risk in clinical drug trials,epidemiological studies, or routine screening. The measures ofproportions or densities could be shown to be useful as markers topredict, for instance, breast cancer risk and possibly risk of diseaserecurrence or change in breast cancer risk.

In order to obtain these measures, techniques have been developed tomaximize the radiographic contrast of tissue composition of a body partto better discriminate cancer risk. The x-ray energies, dose levels, andfilm/screen combinations are typically designed to maximize theradiographic tissue composition contrast. As an example, breast densitywas initially described using a semi-quantitative classification systemthat took into account the quantitative (amount of density) andqualitative nature of the density (diffuse or associated with ductalstructures). Four to ten category systems have been previously used tocover the entire density range. A more quantitative approach measuresthe area of mammographically dense breast area relative to the totalprojected breast area, referred to as mammographic density. Mammographicdensity is a quantitative continuous grading from 0 to 100% densitymeasured by delineating the radiographically dense areas in themammogram from the entire breast area and providing a percentage breastdensity. Although mammographic density is currently a widely usedtechnique, it has serious limitations. First, since the films areuncalibrated for mass density versus film optical density, a uniquethreshold has to be picked for each film. The total and dense projectedareas will change based on the amount of compression. For example, in atypical laboratory, the reproducibility of delineating the dense regionsby an expert radiologist on the same image is approximately 5-7%. Ifboth delineation errors and patient repositioning errors areconservatively assumed to be 7%, the 95% confidence for a significantchange in density is approximately 14%. Thus, the sensitivity for riskclassification and change in follow-up examinations is similar to thatof the categorical methods.

There are many competing methods readily available to estimate body fatbut only a few, Dual Energy X-ray Absorptiometry (DXA), ComputedTomography (CT) and Magnetic Resonance Imaging (MRI) are capable ofmeasuring the tissue composition of specific compartments of the body.CT and MRI work by segmenting the fat from the lean tissue componentsfor individual image planes. Summing all the slices of a whole breastscan to form a volume results in a whole organ % fat mass. The wholeorgan radiation dose of CT limits its usefulness as a screening tool.The overall costs and availability of both CT and MR further limit theirpracticality as a screening tool. For these reasons and its very highprecision (˜300 grams for human whole body measurements and <50 g insmall animals), DXA body composition measurements are the clinicalstandard for whole body and subregional compositional measurements. DXAmeasurements are low dose, typically less than 5 μSv for any procedure,but require the acquisition of two images with beam hardening on thehigher energy image. Prior to the development of DXA, Single EnergyX-ray Absorptiometry (SXA) was used to measure bone density inperipheral bone site such as the forearm. For instance, a forearm wassubmerged in water such that the soft tissue in water provided uniformbackground attenuation. This technique eliminated the problem of softtissue thickness variation and the bone attenuation was then simply theattenuation values above a water/soft tissue threshold.

Accordingly there is a need to develop a more practical device andmethod to quantify proportions or densities of different body materialsin body parts of humans and animals.

SUMMARY OF THE INVENTION

This invention provides generally a radiography device and method. Moreparticularly, the present invention provides a device and method formeasuring proportions of body materials in body parts of humans andanimals. The device and method enables one to determine a proportion ofbody materials in body parts of interest in, for instance, clinical drugtrials and epidemiological cancer risk studies. Measures of body partproportions could be useful as a marker to predict cancer risk andpossibly risk of disease recurrence or change in cancer risk.Furthermore, classification of cancer types could be improved with thedevice and method of the present invention since it provides for a morereproducible and more sensitive approach.

In accordance with exemplary embodiments of the present invention, aradiation device is provided for comparatively determining a proportionof body materials that define a body part. A more detailed embodiment isprovided wherein breast density, as the proportion of body materials ofa breast is determined. The present invention is, however, notrestricted to the use of a breast and could also include other bodyparts of the human and animal body. The radiation device includes adevice for retaining therein the body part in a uniform position. Inaddition, at least two reference materials that have attenuationcharacteristics are used. These reference materials are also retained inthe retaining device. In the example of the breast, the referencematerials represent for instance fat and lean tissue. However, thepresent invention is not limited to the choice of these materials or tothe selection of only two materials. The breast could also be modeled ashaving three or more different materials. The reference materials arebeing positioned in the retaining device for the comparativedetermination during a simultaneous irradiation of the body part and thereference materials. The attenuation characteristics of the referencematerials are selected in correspondence to the attenuationcharacteristics of the body materials in the body part. A radiationmeans for simultaneously irradiating the body part and the referencematerials is used to create attenuated beams of the materials and thebody part. A detector is used to detect and present the attenuated beamsas attenuated values of the materials and the body part. A calculatingmeans, such as a computer, is included for calculating the proportion ofthe body materials that define a particular body part of interest basedon the attenuated values of the materials and the body part.

In view of that which is state above, it is the objective of the presentinvention to provide a device and method that determines a proportion ofbody materials as in for instance a fat and lean ratio of a breast. Itis another objective of the present invention to provide a method anddevice to predict cancer risk and monitor drug trials. The advantage ofthe present invention is that the results obtained by using the deviceand method are irrespective of patient's repositioning errors andreproducible. The device and method are also sensitive in determiningthe proportions of body materials. In addition, the device and method ofthe present invention does not require additional calibration. Finally,the present invention uses just one image of the body part of interest.This enables one to use radiation techniques such as single energy X-rayabsorptiometry as well as single photon absorptiometry. Therefore anadditional advantage is that the use of the present invention reducesthe amount of radiation exposure.

BRIEF DESCRIPTION OF THE FIGURES

The objectives and advantages of the present invention will beunderstood by reading the following detailed description in conjunctionwith the drawings, in which:

FIG. 1 illustrates the general concept of a radiation device and methodaccording to the present invention; and

FIGS. 2-4 illustrates three embodiments of a retaining device and methodaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Although the following detailed description contains many specifics forthe purposes of illustration, anyone of ordinary skill in the art willreadily appreciate that many variations and alterations to the followingexemplary details are within the scope of the invention. Accordingly,the following preferred embodiments of the invention is set forthwithout any loss of generality to, and without imposing limitationsupon, the claimed invention.

The present invention involves a device and method that enables one todetermine a proportion of body materials in body parts of interest in,for instance, clinical drug trials and epidemiological cancer riskstudies. Measures of body part proportions could be useful as a markerto predict cancer risk and possibly risk of disease recurrence or changein cancer risk. For example, promising interventions that may decreasebreast cancer risk such as a low fat diet, phytoestrogens or hormonemanipulations could be first tested by examining whether the proportionof breast area with mammographic densities is affected by theintervention prior to conducting a large randomized controlled trialthat determines the influence on breast cancer incidence. Breast densitycould also be used to identify women at sufficient risk to warranttreatment with SERMS or new agents for prevention of breast cancer. Thepresent invention could also provide a new device and method forclinical and basic scientists to better understand how proliferatedbreast stroma (mammographic breast densities) may interact with breastepithelium to promote growth of breast tumor cells. Furthermore,classification of breast cancer types could be improved with the deviceand method of the present invention since it provides for a morereproducible and more sensitive approach. It is irrespective of patientrepositioning errors and does not need additional calibration.

FIG. 1 shows a simplified flow diagram of the radiation device 100according to the present invention that involves the comparativedetermination of a proportion of body materials 200 defining a body part120. The present invention involves the determination of a proportion200 of, for instance, fat and glandular tissue in a breast. The presentinvention is not limited to the determination of just two materials asit can also, for instance, include materials such as muscle tissue, skintissue, organ tissue, bone tissue, or the like. The choice of theparticular body part 120 of interest is extensive, and not just limitedto a breast. For instance, one can think of different parts ofextremities such as an ear, a tongue, a testicle, skin folds or bodyparts that include a particular organ such as a liver or kidney. The keyidea behind the present invention is that a body part 120 is modeledhaving at least two different materials, such as fat tissue and leantissue in a breast. In general, the part could include a part from ahuman, animal or a plant. Furthermore, the part of the present inventioncould include processed tissue or meat (e.g. grounded beef) or ahomogenized tissue.

The present invention requires one to select at least two referencematerials 130 having attenuation characteristics. The selection of thereference materials 130 is such that the attenuation characteristics arein correspondence to the type of body materials as they are modeled inthe body part 120 of interest. In the case of fat and lean tissue of thebreast, the selection could then be two reference materials 130 havingcorresponding attenuation characteristics to fat and lean. The selectionof the number of materials 130 depends on the type of examination orstudy as well as the level of detail or type of material that is ofinterest to a physician, scientist or epidemiologist.

FIG. 1 also shows a radiation means 110 that simultaneously irradiatesthe body part and the reference materials with beams 115. After passingthrough the body part and reference materials, the beams 115 areattenuated beams 140 and 150 of the body part 120 and the referencematerials 130 respectively. The radiation source 110 provides asimultaneous radiation in order to provide a single image of the bodypart and reference material. In that respect the radiation source 110could for instance be a single energy X-ray absorptiometer (SXA) or asingle photon absorptiometer (SPA). The use of just a single image bymeans of for instance SXA or SPA results in a reduction of the totalamount of radiation exposure to a body part. Other techniques than SXAor SPA to provide a simultaneous radiation are also possible.

The radiation device 100 also includes a detector 160 to detect theattenuated beams 140 and 150 as attenuated values 170 and 180 ofrespectively the body part and reference materials. Preferably, thedetector 160 detects the attenuated values 170 and 180 as a singleimage, but is not limited to a single image since it could also bemultiple images as long as the attenuated values 170 and 180 areavailable for comparison. The detector 160 provides, for instance, afilm or a screen to make an image of the attenuated beams 140 and 150,or a digital device that acquires the attenuated beams 140 and 150 andconvert those into digital values. The detector 160 also includes meansfor presenting or recording the attenuated values 170 and 180 in, forinstance, a color scheme or a gray scale. The idea behind the detector160 is to provide a continuous scale with a large enough resolution forthe attenuation values to identify the selected materials in body part120. Discrete scales are also possible.

The attenuation values 180 of the reference materials 130 are used as areference or calibration for the attenuation values 170 of the body part120 of interest to calculate or determine the proportion 200 of selectedbody materials. For instance, a comparison can be made between thepercentage fat and lean tissue of a breast provided that the attenuationvalues of the breast can be compared with the attenuation values of thefat reference material and lean reference material.

FIG. 1 shows a retaining device 210, as part of the radiation device100, which is shown in more detail in FIGS. 2, 3 and 4. The objective ofthe retaining device 210 is to retain body part 120 in a uniformposition. The uniform position is important to provide a uniformthickness of the materials in body part 120. In addition, retainingdevice 210 also retains at least two reference materials 130 whereby thereference materials 130 being positioned for a comparative determinationduring a simultaneous irradiation by radiation means 110. To make theretaining device 210 also a practical device, a means for adjusting theretaining device 210 could be included to host and retain body parts 120and the materials 130 of various sizes. FIGS. 2, 3, and 4 show differentmechanisms to adjust the position of the retaining device 210. Forexample, wedges 220 and 230 can be used to slide along each other or atelescopic cylinders 240 can be used to telescopically extend or shortento adjust the position.

The retaining device 210 in FIG. 1 could include a cylinder (not shown)to fit and retain the body part 120 and reference materials 130. Theretaining device 210 could also include a system of two paddles 250 and260 to fit and retain the body part 120 and reference materials 130 asshown in FIGS. 2, 3 and 4. Various different configurations and shapescould be designed to serve the same purpose of retaining and hosting ofthe body part 120 and reference materials 130.

The reference materials could be construed as wedges 220 and 230 as inFIG. 2. The reference materials could also be construed in cylindricalcompartments 240 as shown in FIG. 3. The latter is particularly usefulwhen liquids, such as oil and water, are used as reference materials130. In the most general sense, the reference materials 130 could besolids and/or liquids. As mentioned above, the key idea is to select thereference materials so that the attenuation characteristics of thereference materials 130 are equivalent to the attenuationcharacteristics of the selected/modeled body part 120. The solid and/orliquid of the reference material could either represent a fat tissue ora glandular tissue as long as the materials are distinct enough toprovide the necessary resolution to distinguish the modeled materials inthe body part 130. As is shown in FIG. 2 by top view 270, the referencematerials M1 and M2 could be positioned parallel to each other so thatthe beams 115 pass through the reference materials separately. Eachwedge 220 and 230 contains both reference materials M1 and M2. In thiscase the attenuation values 180 are discrete. A similar parallelconfiguration of the reference materials M3 and M4 is shown in FIG. 3 bytop view 272. Alternatively, as shown in FIG. 4 by the top view 274 thereference materials M5 and M6 could be positioned on top of each otherso that the each beam 115 passes through both reference materials 130.The materials could then be made as wedges 222 and 232. In this case theattenuation values 180 provide a more continuous pattern, provided thatthe materials are shaped differently.

The radiating device 100 further comprises means for calculating 190 theproportion of the body materials 200 defining a body part based on thedetected attenuated values 170 and 180. The calculating means could be acomputer based system that is able to receive the attenuated values andcalculate and determine the proportion 200 of body materials of theselected body part 120. A computer system is described for purposes ofexample only. An exemplary embodiment of the invention as describedbelow to calculate the proportion 200 may be implemented in any type ofcomputer system, programming or processing environment. The followingembodiment is an example of the steps that could be included in thecalculating means 190. The exemplary embodiment derives a mammographicdensity based on a single energy X-ray absorptiometry of the breast. Theexample measures the breast tissue on a pixel by pixel basis anddetermines the proportion 200 in terms of percentage fat. The breast inthis particular example is modeled as two materials, i.e. fat andglandular tissue. It would be possible to model the breast as a three ormore compartment model. Summing up all the pixels in the image detectedby detector 160 results in a total fat and glandular mass which could berepresented as a percentage fat mass. The subjective threshold or imageinterpretation would be eliminated. In addition, all the densitometricinformation in the image (gray scale values, color schemes, or the like)would contribute to the measure of the proportion 200, increasing thetechnique's power.

The following equations were derived to quantify SXA tissue density. Asan exemplary embodiment of the present invention, assume that one istaking mammograms with a single energy conical x-ray source 110 using adetector 160 with film screen or direct digital detector. First define %FAT in terms of compression thickness: $\begin{matrix}{{\% \quad {FAT}} = {{\frac{{total\_ fat}{\_ mass}}{total\_ mass}*100} = \frac{\sum\limits_{i,{j = 0}}^{N,M}\quad {w_{f_{i,j}}a_{i,j}\rho_{f}}}{\sum\limits_{i,{j = 0}}^{N,M}\left( {{w_{f_{i,j}}a_{i,j}\rho_{f}} + {w_{l_{i,j}}a_{i,j}\rho_{l}}} \right)}}} & (1)\end{matrix}$

where w_(f) and w_(i) are the compression thickness' of fat and leanrespectively for each pixel, ρ is the component density (fat and lean),ij are the subscripts denoting the rows and columns in the image, N,Marc the total number of rows and columns in an image, and a_(ij) is thecross sectional area of each pixel. The area for each pixel varies as afunction of position due to the cone beam geometry of the device.However each pixel's cross sectional area is known explicitly by devicegeometry of the radiation means 110. The pixel-specific SXA equationrelates the total x-ray attenuation to the attenuation of each componentby:

I _(i,j) =I(0)e ^(−(μ) ^(_(f)) ^(ρ) ^(_(f)) ^(w) ^(_(fi,j)) ^(+μ)^(_(l)) ^(ρ) ^(_(l)) ^(w) ^(_(li,j)) ⁾  (2)

where μ=mass attenuation coefficient (cm²/g) and I(0)=Incident x-rays.In this model, W is the compression thickness and constant:

W=w _(fi,j) +w _(li,j)  (3)

and equation (3) can be substituted into equation (2) to eliminateeither the w_(f) or w_(i). If reference materials 130 are imaged withsimultaneously with the body part (i.e. breast) 120 containing a sample100% fat and 100% glandular tissue at the identical compressionthickness W, equation (2) can be solved to find each pixel's unique μρcombination. For example, in the 100% fat reference, w_(i)=0 such that$\begin{matrix}{{\mu_{f}\rho_{f}} = \frac{- {\ln \left( \frac{I^{\prime}}{I(0)} \right)}}{W}} & (4)\end{matrix}$

where I′ is transmission through fat reference of thickness W. Likewise,in the 100% lean phantom reference, w_(f)=0 and $\begin{matrix}{{\mu_{l}\rho_{l}} = \frac{- {\ln \left( \frac{I^{''}}{I(0)} \right)}}{W}} & (5)\end{matrix}$

where I″ is the transmission through the lean reference of thickness W.Substituting equations (4) and (5) into (2) and solving for w_(f)results in $\begin{matrix}{w_{f_{i,j}} = {\frac{\ln \left( \frac{I_{i,j}}{I^{\prime}} \right)}{\ln \left( \frac{I^{''}}{I^{\prime}} \right)}*W}} & (6)\end{matrix}$

and substituting this into equation (1), the % FAT equation becomes afunction of pixel position, reference material values, the densityratio, and the measured attenuation at each pixel: $\begin{matrix}{{\% \quad {FAT}} = {{\frac{\frac{{\,_{N,M}\ln}\left( \frac{I_{i,j}}{I^{\prime}} \right)}{{\,^{i,{j = 0}}\ln}\left( \frac{I^{''}}{I^{\prime}} \right)}{Wa}_{i,j}\rho_{f}}{\left( {{\frac{{\,_{N,M}\ln}\left( \frac{I_{i,j}}{I^{\prime}} \right)}{{\,^{i,{j = 0}}\ln}\left( \frac{I^{''}}{I^{\prime}} \right)}{Wa}_{i,j}\rho_{f}} + {\left( {W - {\frac{\ln \left( \frac{I_{i,j}}{I^{\prime}} \right)}{\ln \left( \frac{I^{''}}{I^{\prime}} \right)}W}} \right)a_{i,j}\rho_{l}}} \right)}*100} = {\frac{\frac{{\,_{N,M}\ln}\left( \frac{I_{i,j}}{I^{\prime}} \right)}{{\,^{i,{j = 0}}\ln}\left( \frac{I^{''}}{I^{\prime}} \right)}a_{i,j}}{a_{i,j}\left( {\frac{{\,_{N,M}\ln}\left( \frac{I_{i,j}}{I^{\prime}} \right)}{{\,^{i,{j = 0}}\ln}\left( \frac{I^{''}}{I^{\prime}} \right)} + {\left( {1 - \frac{\ln \left( \frac{I_{i,j}}{I^{\prime}} \right)}{\ln \left( \frac{I^{''}}{I^{\prime}} \right)}} \right)\frac{\rho_{l}}{\rho_{f}}}} \right)}*1.00}}} & (7)\end{matrix}$

This derivation is simplified to demonstrate the ideal case. Flat fieldcorrections would have to be taken into account. The calculating means190 could therefore also include means for correcting the attenuationvalues for position dependent variations of the source 110. However, thevariations of the film, x-ray characteristics, developing variations,etc., are all incorporated into the attenuation values of the referencematerials 130 and the body part (i.e. breast) 120. SXA will work for thebreast area at the same height as the reference materials 130 measuredin the same image with the breast 120. In addition, and probably in mostof the cases, there might not be a complete 100% match between thereference materials 130 and the materials in the body part 120. In thatcase a simple ratio or correction factor could be used in thecalculating means to correct for the attenuation values for the materialof interest is determined.

It is important to note that while the calculating means 190 has beendescribed in the context of a functional data processing system andmethod, those skilled in the art will appreciate that the mechanism ofthe present invention is capable of being distributed in the form of acomputer readable medium of instructions in a variety of forms, and thatthe present invention applies equally regardless of the particular typeof signal bearing medium used to actually carry out the distribution.Examples of computer readable medium include: recordable type media suchas floppy disks and CD-ROMS and transmission type media such as digitaland analog communication links. In addition, the present invention couldbe implemented and coded in different programming languages such as, butnot limited to, for example C and C++ programming languages, JAVA orJava script, or DHTML.

The present invention has now been described in accordance with severalexemplary embodiments, which are intended to be illustrative in allaspects, rather than restrictive. Thus, the present invention is capableof many variations in detailed implementation, which may be derived fromthe description contained herein by a person of ordinary skill in theart. All such variations are considered to be within the scope andspirit of the present invention as defined by the following claims andtheir legal equivalents.

What is claimed is:
 1. An apparatus for comparatively determining aproportion of body materials defining a body part, said radiation devicecomprising: (a) at least two reference materials having attenuationcharacteristics, said reference materials being positioned in a uniformposition for said comparative determination during a simultaneousirradiation of said body part and said reference materials, and whereinsaid attenuation characteristics are selected in correspondence to saidbody materials; and (b) a calculating means for calculating saidproportion of said body materials defining a body part based on saidcomparative determination of said materials and said body part.
 2. Theapparatus as set forth in claim 1, wherein said body part comprises abreast and said proportion is a breast density.
 3. The apparatus as setforth in claim 1, wherein said body part comprises an organ and saidproportion is an organ density.
 4. The apparatus as set forth in claim1, wherein said body part comprises bone and said proportion is a bonedensity.
 5. The apparatus as set forth in claim 1, wherein said bodypart comprises muscle and said proportion is a muscle density.
 6. Theapparatus as set forth in claim 1, wherein said body part comprisesprocessed tissue and said proportion is a processed tissue density. 7.The apparatus as set forth in claim 1, wherein said reference materialsare solids.
 8. The apparatus as set forth in claim 7, wherein one ofsaid attenuation characteristics of said reference materials isequivalent to an attenuation characteristic of a fat tissue.
 9. Theapparatus as set forth in claim 7, wherein one of said attenuationcharacteristics of said reference materials is equivalent to anattenuation characteristic of a glandular tissue.
 10. The apparatus asset forth in claim 1, wherein said reference materials are liquidscontained in compartments.
 11. The apparatus as set forth in claim 10,wherein one of said attenuation characteristics of said referencematerials is equivalent to an attenuation characteristic of a fattissue.
 12. The apparatus as set forth in claim 10, wherein one of saidliquids is an oil.
 13. The apparatus as set forth in claim 10, whereinone of said attenuation characteristics of said reference materials isequivalent to an attenuation characteristic of a glandular tissue. 14.The apparatus as set forth in claim 10, wherein one of said liquids is awater.
 15. The apparatus as set forth in claim 1, wherein at least oneof said reference materials is a solid and at least one of saidreference materials is a liquid contained in a compartment.
 16. Theapparatus as set forth in claim 15, wherein said solid has anattenuation characteristic equivalent to a fat tissue and said liquidhas an attenuation characteristic equivalent to a glandular tissue. 17.The apparatus as set forth in claim 16, wherein said liquid is a water.18. The apparatus as set forth in claim 15, wherein said liquid has anattenuation characteristic equivalent to a fat tissue and said solid hasan attenuation characteristic equivalent to a glandular tissue.
 19. Theapparatus as set forth in claim 18, wherein said liquid is an oil. 20.The apparatus as set forth in claim 1, wherein said reference materialsare construed as blocks.
 21. The apparatus as set forth in claim 1,wherein said reference materials are construed as wedges.
 22. Theapparatus as set forth in claim 1, wherein said reference materials areconstrued in cylindrical compartments.
 23. The apparatus as set forth inclaim 1, further comprising a device for retaining therein said bodypart in said uniform position.
 24. The apparatus as set forth in claim23, wherein said retaining device further comprises means for adjustingto host and retain said body part and said materials of various sizes.25. The apparatus as set forth in claim 1, further comprising aradiation means for simultaneously irradiating said body part and saidreference materials thereby creating attenuated beams of said materialsand said body part.
 26. The apparatus as set forth in claim 25, whereinsaid radiation means is a single energy X-ray absorptiometer.
 27. Theapparatus as set forth in claim 25, wherein said radiation means is asingle photon absorptiometer.
 28. The apparatus as set forth in claim25, further comprising a detector to detect said attenuated beams asattenuated values of said materials and said body part.
 29. Theapparatus as set forth in claim 28, wherein said detector presents saidattenuated beams in attenuation values.
 30. The apparatus as set forthin claim 28, wherein said attenuation values are presented by saiddetector according to a color scheme.
 31. The apparatus as set forth inclaim 28, wherein said attenuation values are presented by said detectoraccording to a gray scale.
 32. The apparatus as set forth in claim 28,wherein said calculating means further comprises means for correctingsaid attenuation values for position dependent variations of saidradiation means.
 33. A method for comparatively determining a proportionof body materials defining a body part, said radiation devicecomprising: (a) providing at least two reference materials havingattenuation characteristics, said reference materials being positionedin a uniform position for said comparative determination during asimultaneous irradiation of said body part and said reference materials,and wherein said attenuation characteristics are selected incorrespondence to said body materials; and (b) providing a calculatingmeans for calculating said proportion of said body materials defining abody part based on said comparative determination of said materials andsaid body part.
 34. The method as set forth in claim 33, wherein saidbody part comprises a breast and said proportion is a breast density.35. The method as set forth in claim 33, wherein said body partcomprises an organ and said proportion is an organ density.
 36. Themethod as set forth in claim 33, wherein said body part comprises boneand said proportion is a bone density.
 37. The method as set forth inclaim 33, wherein said body part comprises muscle and said proportion isa muscle density.
 38. The method as set forth in claim 33, wherein saidbody part comprises processed tissue and said proportion is a processedtissue density.
 39. The method as set forth in claim 33, wherein saidreference materials are solids.
 40. The method as set forth in claim 39,wherein one of said attenuation characteristics of said referencematerials is equivalent to an attenuation characteristic of a fattissue.
 41. The method as set forth in claim 39, wherein one of saidattenuation characteristics of said reference materials is equivalent toan attenuation characteristic of a glandular tissue.
 42. The method asset forth in claim 33, wherein said reference materials are liquidscontained in compartments.
 43. The method as set forth in claim 42,wherein one of said attenuation characteristics of said referencematerials is equivalent to an attenuation characteristic of a fattissue.
 44. The method as set forth in claim 42, wherein one of saidliquids is an oil.
 45. The method as set forth in claim 42, wherein oneof said attenuation characteristics of said reference materials isequivalent to an attenuation characteristic of a glandular tissue. 46.The method as set forth in claim 42, wherein one of said liquids is awater.
 47. The method as set forth in claim 33, wherein at least one ofsaid reference materials is a solid and at least one of said referencematerials is a liquid contained in a compartment.
 48. The method as setforth in claim 47, wherein said solid has an attenuation characteristicequivalent to a fat tissue and said liquid has an attenuationcharacteristic equivalent to a glandular tissue.
 49. The method as setforth in claim 48, wherein said liquid is a water.
 50. The method as setforth in claim 47, wherein said liquid has an attenuation characteristicequivalent to a fat tissue and said solid has an attenuationcharacteristic equivalent to a glandular tissue.
 51. The method as setforth in claim 50, wherein said liquid is an oil.
 52. The method as setforth in claim 33, wherein said reference materials are construed asblocks.
 53. The method as set forth in claim 33, wherein said referencematerials are construed as wedges.
 54. The method as set forth in claim33, wherein said reference materials are construed in cylindricalcompartments.
 55. The method as set forth in claim 33, furthercomprising the step of providing a device for retaining therein saidbody part in said uniform position.
 56. The method as set forth in claim55, wherein said step of providing retaining device further comprisesthe step of providing means for adjusting to host and retain said bodypart and said materials of various sizes.
 57. The method as set forth inclaim 33, further comprising the step of providing a radiation means forsimultaneously irradiating said body part and said reference materialsthereby creating attenuated beams of said materials and said body part.58. The method as set forth in claim 57, wherein said radiation means isa single energy X-ray absorptiometer.
 59. The method as set forth inclaim 57, wherein said radiation means is a single photonabsorptiometer.
 60. The method as set forth in claim 57, furthercomprising the step of providing a detector to detect said attenuatedbeams as attenuated values of said materials and said body part.
 61. Themethod as set forth in claim 60, wherein said detector presents saidattenuated beams in attenuation values.
 62. The method as set forth inclaim 60, wherein said attenuation values are presented by said detectoraccording to a color scheme.
 63. The method as set forth in claim 60,wherein said attenuation values are presented by said detector accordingto a gray scale.
 64. The method as set forth in claim 60, wherein saidcalculating means further comprises means for correcting saidattenuation values for position dependent variations of said radiationmeans.
 65. An apparatus for comparatively determining a proportion ofmaterials defining a part wherein said part is a human part, animalpart, plant part, a processed tissue part or a homogenized tissue part,said radiation device comprising: (a) at least two reference materialshaving attenuation characteristics, said reference materials beingpositioned in a uniform position for said comparative determinationduring a simultaneous irradiation of said part and said referencematerials, and wherein said attenuation characteristics are selected incorrespondence to said materials; and (b) a calculating means forcalculating said proportion of said materials defining a part based onsaid comparative determination of said materials and said part.
 66. Amethod for comparatively determining a proportion of materials defininga part wherein said part is a human part, animal part, plant part, aprocessed tissue part or a homogenized tissue part, said radiationdevice comprising: (a) providing at least two reference materials havingattenuation characteristics, said reference materials being positionedin a uniform position for said comparative determination during asimultaneous irradiation of said part and said reference materials, andwherein said attenuation characteristics are selected in correspondenceto said materials; and (b) providing a calculating means for calculatingsaid proportion of said materials defining a part based on saidcomparative determination of said materials and said part.